Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Seawater samples were collected on R/V Atlantis (AT15-61) cruise in Jan-Feb 2010 and on R/V Melville (MV1104) cruise in Mar-Apr 2011.  Water samples were collected at discrete depths using Niskin bottle type rosette samplers equipped with either 24 bottles (10L) or 12 bottles (20L), and an SBE9plus conductivity-temperature-depth (CTD) sensor package (SeaBird Electronics, Bellevue, WA).  

(All data are downcast sensor data only).

Downcast CTD sensor data were processed using Seabird Electronics (SBE) Data Processing software using SBE recommended parameters, including the tau oxygen correction and oxygen hysteresis correction.  Processing commands were applied in the following order:  filter, alignctd, celltm, loopedit, wildedit.  After manual inspection of the data, in the 2011 dataset, oxygen values were advanced 3 sec relative to the temperature data to minimize spiking around large gradients in dissolved oxygen. Data were binned at 1 m depth intervals.

Note: Missing data values for longitude (and other fields) are due to instrument aberration during collection

BCO-DMO data processing:

• Added a conventional header with dataset name, PI names, version date
• Concatenated individual files of binned data from two cruises
• Replaced missing values with 'nd' ('nd' is BCO-DMO's default missing data identifier)
• Replaced any -9.99e-29, -9.99e-28, -9.99e-27, +9.99e-29, +9.90e-27, -9.90e-28 values with 'nd'
• Created Cruise and Cast columns based on filenames, and put filename in separate column
• Added ISO DateTime UTC field for each cast with times from raw CTD files (as found in R2R)

Description from NSF award abstract:
Closing the marine budgets of nitrate and nitrous oxide are central goals for researchers interested in nutrient-driven changes in primary productivity and climate change. With the implementation of new methods for oxygen isotopic analysis of seawater nitrate, it will be possible to construct a budget for nitrate based on its oxygen isotopic distribution that is complementary to nitrogen isotope budgets. Before we can effectively use oxygen isotopes in nitrate to inform the current understanding of the marine nitrogen cycle, we must first understand how different processes that produce (nitrification) and consume (assimilation, denitrification) nitrate affect its oxygen isotopic signature.

In this study, researchers at the Woods Hole Oceanographic Institution will provide a quantitative assessment of the oxygen isotopic systematics of nitrification in the field and thus fill a key gap in our understanding of 18O variations in nitrate, nitrite, and nitrous oxide. The primary goal is to develop a quantitative prediction of the oxygen isotopic signatures of nitrite and nitrate produced during nitrification in the sea. The researchers hypothesize that oxygen isotopic fractionation during nitrification is the primary factor setting the 18O values of newly produced nitrate and nitrite. Secondly, they hypothesize that oxygen atom exchange is low where ammonia oxidation and nitrite oxidation are tightly coupled, but may increase in regions with nitrite accumulation, such as in the primary and secondary nitrite maxima. They will test these hypotheses with a series of targeted laboratory and field experiments, as well as with measurements of nitrite and nitrate isotopic distributions extending through the euphotic zone, primary nitrite maximum, and secondary nitrite maximum of the Eastern Tropical South Pacific. The results of these experiments are expected to provide fundamental information required for the interpretation of 18O isotopic signatures in nitrite, nitrate, and N2O in the context of underlying microbial processes. A better understanding of these features and the processes involved is important for quantifying new production, controls on the N budget, and N2O production in the ocean -- which should lead to a better understanding of the direct and indirect interactions among the nitrogen cycle, marine chemistry, and climate.